To change your podcast publishing platform (such as onboarding to Megaphone from another hosting provider), you typically will issue a 301 redirect to permanently move the RSS feed from one source to another.
A helpful explainer from elsewhere on the web...
A 301 redirect is a permanent redirect which passes between 90-99% of link juice (ranking power) to the redirected page. 301 refers to the HTTP status code for this type of redirect. In most instances, the 301 redirect is the best method for implementing redirects on a website.
For more info on redirecting your podcast(s), visit our Redirecting to Megaphone section in the Help Center.